Internal combustion engines with cylinder benches of light metal alloys arranged in V-shape or in line with respect to each other are often fabricated using low-pressure die casting methods or gravity casting methods. Filling is typically performed with the crankcase standing upright, the cylinder being at the top, while the bearing bracket is situated at the bottom. It is further known to arrange the crankcases in a lying position during casting and to arrange the gates at the sides so as to be able to cool the bearing brackets and cylinder walls for an improved structure, as described, for example, in DE 10 2006 030 129 A1.
When casting in an upright state, the melt solidifies either from the cylinder head side towards the crank space or vice versa depending on the point of introduction of the melt into the cavity of the mold. In this regard, either the cylinder deck or the bearing brackets solidify more slowly than the respective other part, resulting in a coarser structure with reduced strength in the parts solidifying more slowly. Relatively long solidification paths further result from the arrangement of the gates, which in turn results in high tool temperatures necessary to provide a correct filling of the mold without formation of blowholes. Another difficulty when designing is to avoid a complete blocking of the feed path by the inner cores during casting, the number and complexity of the cores increasing in modern internal combustion engines.
In an attempt to provide the greatest possible bearing bracket strength via short solidification times, it has been suggested to fill the cylinder crankcase from below using the low-pressure method with the cylinder deck situated at the bottom and the bearing bracket in the upper region. EP 1 498 197 A1, for example, describes casting a crankcase for V-shaped internal combustion engines in an upside down orientation and to introduce the melt from below, i.e., from the cylinder side. To prevent blowholes, feeders are arranged outside the cavity forming the cylinder crankcase. Due to the upward directed movement towards the bearing bracket, the melt is in a cooled state near the eutectic temperature when it reaches the region of the bearing bracket where high cooling speeds result which, in turn, lead to a fine structure with small dendrite arm spacings. A fast solidification at the cylinder deck cannot, however, be achieved. The strength in the region of the bolt bosses is also insufficient since blowholes may form due to insufficient feed to these regions.
A low-pressure casting method for internal combustion engines with cylinders arranged in a V-shape is also described in DE 10 2011 056 985 A1 wherein the orientation for casting is selected so that the cylinders are directed downward to the gate. Casting is performed on the sides of the cylinders facing each other. The cylinders may be cooled using chill molds so that small dendrite arm spacings can be achieved both in the bearing bracket area and at the cylinder walls. The supply of melt to the large-volume parts of the cylinder crank case is, however, insufficient, in particular due to shrinking processes during cooling, so that insufficient strength is achieved in these regions or in the region of the bolt pipes.
No method is therefore currently known with which it is possible to achieve both small dendrite arm spacings in the region of the bearing bracket and the cylinder bore surfaces at the web regions and a high strength by avoiding blowholes in the region of the bolt bosses.